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Sound-Level Measurements

Can CPUs Make PCs Faster & Quieter?
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As we mentioned above, a PC that operates in the range from 20-25 dBA counts as "extremely quiet," if not silent to all intents and purposes, while 25-30 dBA is very quiet and 30-45 dBA is somewhat audible. By this rough metric, both of our test builds fall in that last category.

We provide a chart of results, and include the same numbers for one of the writer's desktop PCs as a point of comparison. But first, let's discuss placement of the SLM for the measurements we present and why this makes a difference. We set up the SLM over three feet away from the PC, with the exhaust fans facing away from the meter (on the far side of the case blowing away), then with the exhaust fans facing toward the meter (on the near side of the case blowing toward). Then we took measurements with the meter on top of the PC.

The difference between exhaust on the far and near sides is clear in the numbers that show up: the noise levels drop with distance from the exhaust ports. Predictably, the values recorded for the meter on top of the case fall between the other two values, because the sound path is longer than that for the near side and shorter than that for the far side.

To understand the impact of the case itself on sound levels measured, we also took the side panels off and took measurements with the fan blowing toward the SPM, and on top of the case.

Noise level measurements (in dBA)
System Fan far Fan near Top Fan near, open Top, open
T7600 35.2 37.3 35.9 36.8 35.6
QX6800 37.5 38.1 38.3 40.4 37.7
Delta 2.3 0.8 2.4 3.6 2.1
Desktop 39.8 39.6 39.7 42.0 39.0

By these measurements, these systems qualify as suitable even in a quiet office or a library. Both builds are quieter than a desktop on which one of the authors of this story has expended considerable effort to quiet down, including switching to a quieter CPU cooler, replacing all case fans with the quietest models available, and additional work on case baffles and lengthening the sound path. We also believe they are as quiet, if not quieter, than the majority of media PCs we've built and evaluated. But according to standard metrics for PC noise, it's important to emphasize that both the T7600 and QX6800 builds qualify only as "somewhat quiet" instead of as "quiet."

That said, we also find it interesting that there's very little difference in sound output between the more-powerful system and the less-powerful one. The biggest meaningful difference (we don't consider the door-open measurements to be informative, except in showing the impact of the case in directing sound away from the user) occurs in the measurement from the top of the case. This is a position similar to the one in which the user is likely to be if the case is slid underneath a desk to their right or left. The difference between our two measurements was 2.4 dBA," rather than the current wording (because it's a difference, not really a direct measurement by itself).

In terms of characterizing the sound output from each build, we'd rank the T7600 as a little bit quieter than the QX6800. But the sound from the T7600 was a little higher in pitch than that of the QX6800, probably because of the 70 mm CPU cooler fan in the former versus the 92 mm fan in the latter. For both systems, we'd categorize the sound as a slight whirring noise, definitely associated with the four case fans and the CPU cooler fans in use. Neither was objectionably or noticeably loud, and both contributed little background noise in our normal working environment.

In short, both of these PCs qualify as fairly quiet, and seem to make a case that the trend toward lower CPU power consumption and heat release from CPUs is having a salutary effect on PC noise output.

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